MaterialsgateNEWS
2017/02/16

Related MaterialsgateCARDS

Learning how to fine-tune nanofabrication

A new computational method may improve the control of nanomaterial fabrication

Daniel Packwood, Junior Associate Professor at Kyoto University's Institute for Integrated Cell-Material Sciences (iCeMS), is improving methods for constructing tiny "nanomaterials" using a "bottom-up" approach called "molecular self-assembly". Using this method, molecules are chosen according to their ability to spontaneously interact and combine to form shapes with specific functions. In the future, this method may be used to produce tiny wires with diameters 1/100,000th that of a piece of hair, or tiny electrical circuits that can fit on the tip of a needle.

Molecular self-assembly is a spontaneous process that cannot be controlled directly by laboratory equipment, so it must be controlled indirectly. This is done by carefully choosing the direction of the intermolecular interactions, known as "chemical control", and carefully choosing the temperature at which these interactions happen, known as "entropic control".

Researchers know that when entropic control is very weak, for example, molecules are under chemical control and assemble in the direction of the free sites available for molecule-to-molecule interaction. On the other hand, self-assembly does not occur when entropic control is much stronger than the chemical control, and the molecules remain randomly dispersed.

Until now, it's not been possible for researchers to guess what kinds of structures will result from molecular self-assembly when entropic control is neither weak nor strong compared to chemical control.

Packwood teamed up with colleagues in Japan and the U.S. to develop a computational method that allows them to simulate molecular self-assembly on metal surfaces while separating the effects of chemical and entropic controls.

This new computational method makes use of artificial intelligence to simulate how molecules behave when placed on a metal surface. Specifically, a "machine learning" technique is used to analyse a database of intermolecular interactions. This machine learning technique builds a model that encodes the information contained in the database, and in turn this model can predict the outcome of the molecular self-assembly process with high accuracy.

The team used this method to study the self-assembly of three different hydrocarbon molecules, the structures of which vary in the strength of the direction of their intermolecular interactions. In other words, they varied the strength of chemical control by changing the molecule under study.

While stronger chemical control caused molecules to assemble into chain-shaped structures, the effects of stronger entropic controls were found to be more counterintuitive. For example, they found that strengthening entropic control could transform large, disordered structures into several small, ordered, chain-shaped structures. They also showed that the formation of disordered structures results from weak chemical control rather than strong entropic control.

These predictions, which were verified by comparisons with high-resolution microscopic images of real molecules on metal surfaces, may lead to controlled, large-scale fabrication of tiny electrical wires and other nanomaterials for future devices. Devices made from nanomaterials would be significantly smaller and cheaper than existing electronics, and would have very long battery lives due to low energy consumption.

"By continued development of our code and theory, we expect to obtain increasingly detailed rules for controlling molecular self-assembly and aiding the bottom-up nanomaterials fabrication process," the researchers conclude in their study published in the journal Nature Communications.

Source: Kyoto University – 14.02.2017.

The paper "Chemical and Entropic Control on the Molecular Self-Assembly Process" appeared on February 14, 2017 in Nature Communications, with doi: 10.1038/ncomms14463

Investigated and edited by:

The investigation and editing of this document was performed with best care and attention.
For the accuracy, validity, availability and applicability of the given information, we take no liability.
Please discuss the suitability concerning your specific application with the experts of the named company or organization.

You want additional material or technology investigations concerning this subject?

These are potential applications for a thin, flexible, light-absorbing material developed by engineers at the University of California San Diego.
The material, called a near-perfect broadband absorber, absorbs more than 87 percent of near-infrared light (1,200 to 2,200 nanometer wavelengths), with 98 percent absorption at 1,550 nanometers, the wavelength for fiber optic communication. The material is capable of absorbing light from every angle. It also can theoretically be customized to absorb certain wavelengths of light while letting others pass through.
Materials that "perfectly" absorb light already exist, but they are bulky and can break when bent. They also cannot be controlled... more

The same researchers who pioneered the use of a quantum mechanical effect to convert heat into electricity have figured out how to make their technique work in a form more suitable to industry.

In Nature Communications, engineers from The Ohio State University describe how they used magnetism on a composite of nickel and platinum to amplify the voltage output 10 times or more—not in a thin film, as they had done previously, but in a thicker piece of material that more closely resembles components for future electronic devices.
Many electrical and mechanical devices, such as car engines, produce heat as a byproduct of their normal operation. It’s called “waste heat,” and its existence is required by the fundamental laws of thermodynamics, explained study co-author Stephen Boona.
But a growing area of research called solid-state thermoelectrics aims to capture that waste... more

Rice University theory shows way to enhance heat sinks in future microelectronics

Bumpy surfaces with graphene between would help dissipate heat in next-generation microelectronic devices, according to Rice University scientists.
Their theoretical studies show that enhancing the interface between gallium nitride semiconductors and diamond heat sinks would allow phonons - quasiparticles of sound that also carry heat - to disperse more efficiently. Heat sinks are used to carry heat away from electronic devices.
Rice computer models replaced the flat interface between the materials with a nanostructured pattern and added a layer of graphene, the atom-thick form of carbon, as a way to dramatically improve heat transfer, said Rice materials scientist Rouzbeh Shahsavari... more

One of the most promising innovations of nanotechnology has been the ability to perform rapid nanofabrication using nanometer-scale tips. The fabrication speed can be dramatically increased by using heat. High speed and high temperature have been known to degrade the tip… until now.

“Thermal processing is widely used in manufacturing,” according to William King, the College of Engineering Bliss Professor at Illinois. “We have been working to shrink thermal processing to the nanometer scale, where we can use a nanometer-scale heat source to add or remove material, or induce a physical or chemical reaction.”
One of the key challenges has been the reliability of the nanometer-scale tips, especially with performing nano-writing on hard, semiconductor surfaces. Now, researchers at the University of Illinois, University of Pennsylvania, and Advanced Diamond Technologies Inc., have created a new type of nano-tip for thermal processing, which is made entirely out of... more